The Adaptive bit is greyed out because the sub
assembly file is currently selected as being adaptively used in an
assembly. Open the sub assembly, goto Tools -> Document settings ->
Modelling tab and uncheck "Adaptively used in assembly"
Just remember that this sub assembly change in the
other assembly that it is in. You would also be getting errors when you
open the other assembly because it will try to resolve whatever constraints you
have on it. Have you thought about duplicating the sub assembly with one
for each assembly?
Another problem arises if the subassembly is used more then once in the same assembly, if you want different behaviors for each sub assy, all must be different copies. Kinda (edited) but the behavior is logical.